Method of α-selective glycosylation

ABSTRACT

An α-selective glycosylation process of a glycosylation reaction between a sugar structure of hexose or an aldose having a chain with six or more carbon atoms in the molecule, which is a monosaccharide or a reducing end of an oligosaccharide with two or more monosaccharide residues connected by glycosidic linkages (an oligosaccharide with two monosaccharide residues is disaccharide) (also referred to as “a disaccharide to an oligosaccharide”) or a sugar chain and alcoholic hydroxyl group or thiol group, to obtain a sugar structure glycoside containing α-glycoside at a high ratio, under the ring-shaped formation of a protective group in a silyl acetal structure over hydroxyl groups at positions 4 and 6 in the sugar structure. 
     By the process, highly selective α-glycosylation of sugar structure can be progressed in a simple and efficient manner.

TECHNICAL FIELD

The present invention relates to an α-selective glycosylation process.More specifically, the invention relates to an α-selective glycosylationprocess of sugar structures with galactose and other given essentialstructures, and derivative compounds thereof, or oligosaccharides withtwo or more monosaccharide residues connected by glycosidic linkages(oligosaccharide with two monosaccharide residues is disaccharide)(referred to as “disaccharides to oligosaccharides” hereinbelow) orsugar chains, having these sugar structures and derivative compoundsthereof at their reducing ends.

BACKGROUND ART

In recent years, particularly in the post-genome era, sugarchain-containing polymers existing as intracellular and extracellularmembrane constituents and extracellular molecules in multi-cellularbiological organisms, particularly higher biological organisms havedrawn attention in relation with the functions thereof in suchbiological organisms. One typical example of the sugar chain-containingpolymers is glycoprotein.

With some exceptions, most of cellular surface membranes and serumproteins in many animals primarily including humans are glycoproteins.For example, antibodies, receptors, hormones and enzymes are not simpleproteins but are commonly glycoproteins. The functions of suchglycoproteins in biological organisms have traditionally been describedfrom the standpoint of protein structure alone. Since the fact was foundthat the specificities of ABO (H) type-blood group antigens aredetermined on the basis of the subtle difference in their sugar chainmoieties, however, the roles of sugar chains in glycoproteins as signalshave increasingly been focused in relation with various discriminationphenomena required for the establishment and retention of multi-cellularbiological organisms.

Specifically, a protein is expressed on the basis of a geneticinformation and is then glycosylated (added with a sugar chain), to givea biological selectivity extremely specific to the function of theprotein itself to the resulting glycoprotein. Glycoproteins are widelydistributed in tissues and organisms of animals and plants. Due to thesignificance of the sugar chains in glycoproteins, diverse and enormousresearch works have been done and accumulated, for example researchworks about tumor specific antigens derived from sugar chains.Concurrently, the analysis of sugar chain structures (sequences andsteric structures thereof) has made a great progress.

Sugar chains of glycoproteins are broadly classified in N-glycosidelinkage type (Asn linkage type) where the sugar chains are linked toL-asparagine as an amino acid residue composing polypeptides and inO-glycoside linkage type (O linkage type) where the sugar chains arelinked to L-serine or L-threonine. Among them, sugar chains of O linkagetype are found in a wide range including for example various mucousproteins, serum proteins and membrane proteins. Typically, such sugarchains of O linkage type form α-O-glycoside linkage via a nucleophilicreaction using N-acetyl-D-galactosamine as the donor and the alcoholichydroxyl group of L-serine or L-threonine as the acceptor.

For research works and analyses about the sugar chains of glycoproteinsor about lectin drawing attention as a functional protein specificallyrecognizing the sugar chains of glycoproteins, for example, glycoproteinsamples should be prepared at an amount of about several micrograms ormore. Because the intended glycoproteins exist at an extremely traceamount in the order of nanogram/milliliter in tissues and cells ofanimals and plants, generally, the preparation of needed amounts ofglycoprotein samples is laborious.

Therefore, research works about the chemical synthesis of glycoproteinsof Asn linkage type and O linkage type have been done intensivelyworldwide. Setting research works about the chemical synthesis ofglycoproteins of Asn linkage type aside, various approaches for thechemical synthesis of the glycoproteins of O linkage type have beenproposed in terms of O-glycoside linkage very common in the field ofsugar chemistry according to techniques developed for the glycosylationof sugar residues together.

The chemical synthesis of glycoproteins of O linkage type involves avery difficult problem as to how the glycosylation between galactosamineat the reducing end and the alcoholic hydroxyl group of amino acid canbe facilitated in an α-selective manner. In the glycosylation ofN-acetyl-D-galactosamine, in other words, the N-acetylamino group atposition 2 interferes with the glycosylation through the neighboringgroup participation. Accordingly, β-glycosylation also occurs at aconsiderable ratio, disadvantageously.

Paulsen, et al. propose a process using a 2-azide derivative so as tocope with the disadvantage. As shown in FIG. 1, the process includes thestereo-specific cleavage of 1,6;2,3-dianhydrosugar (i) with azide anionto prepare 2-azide (ii), the conversion of the resulting 2-azide tosynthetically prepare α-bromide (iv), and the treatment of the resultingα-bromide with tetraethylammonium chloride to prepare β-chloride (v), tothereby prepare α-glycoside under the Koenigs-Knorr reaction conditions.

A simple synthetic process of 2-azide sugar was then developed byLemieux and Ratcliffe. As shown in FIG. 2, Ferrari and Pavia convertedthe compound (x) obtained by the synthetic process to β-chloride (xi),which was then condensed with an L-serine derivative, using a mercurysalt as a promoter, to obtain α-glycoside (xii) at a yield of 66%.

Furthermore, Paulsen, et al. utilized silver perchlorate and silvercarbonate (at a ratio of 1:10) as the promoter in a non-polar mixturesolvent of methylene chloride/toluene so as to suppress unnecessaryanomerization of the compound (xi) in FIG. 2. The process produced afruitful result of the yield of 85% and the α selectivity/β selectivityratio of 19:1.

The various synthetic processes described above, particularly theprocess of Paulsen, et al. using silver perchlorate and silver carbonateas the promoter produced a very great result from the standpoint of theissue of the (α-selective glycosylation. However, the processes havecommon disadvantages of poor practical wide applicability in view ofdonor preparation stage and tough reaction control.

SUMMARY OF THE INVENTION

It is an object of the invention to enable highly selectiveα-glycosylation of given sugar structures including the chemicalsynthesis of glycoproteins of O linkage type by a simple and convenientapproach.

The present inventors found that highly selective α-glycosylation ofsugar chain acceptors could be generated, by simply forming a protectivegroup in a silyl acetal structure on a predetermined hydroxyl group in asugar structure such as galactose.

In a first aspect of the invention, an α-selective glycosylation processbetween a sugar structure as a donor and an alcoholic hydroxyl group orthiol group as an acceptor compound, using as the sugar structure asugar structure of hexose or an aldose having a chain with seven or morecarbon atoms in the molecule, which is a monosaccharide or a reducingend of an oligosaccharide with two or more monosaccharide residuesconnected by glycosidic linkages (oligosaccharide with twomonosaccharide residues is disaccharide) (also referred to as “adisaccharide to an oligosaccharide” hereinbelow) or a sugar chain andwhich should essentially satisfy the constitutional conditions such thatthe sugar structure has hydroxyl groups at least at positions 4 and 6and that the hydroxyl group at position 4 is in an axial bond and agroup at position 5 is in equatorial bond, comprises the followingsteps:

-   (1) a step of forming a protective group in a silyl acetal structure    in a ring shape over the hydroxyl groups at positions 4 and 6 in the    sugar structure, and-   (2) a step of promoting the glycosylation between the sugar    structure and the alcoholic hydroxyl groups or thiol group, to    prepare a sugar structure glycoside containing α-glycoside at a    ratio of 80% or more in the ratio of α- /β-glycosides.

According to the α-selective glycosylation process in the first aspectof the invention, highly selective α-glycosylation can be progressed bya very simple approach including the formation of a protective group ina silyl acetal structure in a ring shape over the hydroxyl groups atpositions 4 and 6 in a given sugar structure and subsequentglycosylation between the sugar structure and the alcoholic hydroxylgroup or thiol group as an acceptor compound. The ratio of α-anomer inthe resulting glycoside is generally 80% or more.

At synthetic experiments where the inventors found the effect,2,2,2-trichloroethoxycarbonyl group (Troc group) and the like existedother than the protective group in the silyl acetal structure inN-acetylgalactosamine as the donor, while the acceptor compound wasdisialylgalactose. As described below in the following Examples, theinventors verified through sequential verification experiments aboutthese individual elements that the formed protective group in the silylacetal structure enabled the highly α-selective glycosylation.

As described below, the α-selective glycosylation process is neveraffected by any interference of N-acetylamino group with glycosylation,which has been a problem in the chemical synthesis of glycoproteins of Olinkage type. Compared with the previous techniques proposed from thesame standpoint, for example the process using 2-azide derivatives byPaulsen et al. and the modified process of Ferrari and Pavia, thepresent process is a chemical synthetic process with a practicalapplicability, only requiring very simple procedures. Therefore,glycoproteins as research samples for the research works and analysis ofthe sugar chains of glycoproteins, lectin and the like have successfullybeen prepared by such simple chemical synthesis.

Additionally, the α-selective glycosylation process in the first aspectof the invention can generally been established between a sugarstructure (donor) provided with given conditions and an acceptorcompound having at least an alcoholic hydroxyl group or thiol group butis never limited to the synthesis of glycoproteins of O linkage type. Inother words, the donor may satisfactorily be a monosaccharide or anoligosaccharide while amino acids, peptide chains, monosaccharides,sugar chains and other types of appropriate organic compounds may beused as the acceptor compound as long as these compounds have alcoholhydroxyl group or thiol group.

In a second aspect of the invention, the sugar structure according tothe α-selective glycosylation process in the first aspect of theinvention is any one of those (a) to (d) described below.

-   (a) D-Galactose or L-galactose-   (b) D-Gulose or L-gulose-   (c) 2-Deoxy-D-galactose or 2-deoxy-L-galactose-   (d) Heptose with an essential structure of any one of (a) through    (c).

According to the α-selective glycosylation process, the sugar structureas the donor essentially satisfies the given constitutional conditionsdescribed in the first aspect. Typical sugar structures satisfying theconstitutional conditions are any one of the sugar structures describedas (a) to (d) in the second aspect.

In a third aspect of the invention, the sugar structure according to theα-selective glycosylation process in the first or second aspect of theinvention takes C1 steric conformation (⁴C₁ pyranoside structure) whenthe sugar structure is in the D form or the sugar structure takes 1Csteric conformation (¹C₄ pyranoside structure) when the sugar structureis in the L form.

Particularly preferably, the sugar structure in the D form as the donortakes C1 steric conformation and the sugar structure in the L form takes1C steric conformation, because these conformations are preferentialconformations, respectively. A possibility cannot be denied however thatthe sugar structure in the D form taking 1C steric conformation and thesugar structure in the L form taking C1 steric conformation also expressthe actions and advantages of the first aspect of the invention.

In a fourth aspect of the invention, the protective group in the silylacetal structure according to the α-selective glycosylation process inany one of the first to third aspects of the invention isdialkylsilylene group.

The protective group in a ring shape as formed over the hydroxyl groupsat positions 4 and 6 in the sugar structure can preferably form adialkylsilylene group, with no specific limitation, as long as theprotective group is in the silyl acetal structure.

In a fifth aspect of the invention, the dialkylsilylene group accordingto the α-selective glycosylation process in the fourth aspect of theinvention is di-(t-butyl)-silylene group (DTBS group).

As the dialkylsilylene group, di-(t-butyl)-silylene group (DTBS group)is particularly preferable.

In a sixth aspect of the invention, reactive functional groups exceptthe hydroxyl groups at positions 4 and 6 in the sugar structure arepreliminarily treated with protective group modification, before theformation of the protective group in the silyl acetal structureaccording to the α-selective glycosylation process in any one of thefirst to fifth aspects of the invention.

The treatment for the modification with given protective groupsaccording to the sixth aspect of the invention effectively suppressesunnecessary side reactions for the formation of the protective group inthe silyl acetal structure in the sugar structure or for the subsequentα-selective glycosylation. For adding another sugar and the like to aspecific functional group in a sugar or an amino acid or the like as theconstitutional part of the donor or the acceptor, further, thefunctional group is effectively modified with another protective group,which can be eliminated with not any influence on other protectivegroups.

In a seventh aspect of the invention, the protective group of the aminogroup for the protective group modification according to the α-selectiveglycosylation in the sixth aspect of the invention is2,2,2-trichloroethoxycarbonyl group (Troc group).

In case that the sugar structure contains an amino group (at position 2in particular), for example in case that the amino group in an aminosugar such as galactosamine and glucosamine is to be protected,phthaloyl group (Phth group) has frequently been used previously.However, Phth group is at such a low introduction efficiency that Phthgroup is not appropriate for mass-scale synthesis. In case that cyanuricacid and the like concurrently exist in the reaction system, forexample, hydrazine is generally used for removing the Phth group. So asto avoid the generation of amides due to the attack thereof to themethyl ester, the methyl ester is once removed. Subsequently, freecarboxylic acid is again prepared into methyl ester. Such laboriousworks for deprotection are essentially required. Concerning thesepoints, the inventors found that protection of amino group with Trocgroup was suitable from the standpoint of efficient synthesis ofα-glycoside.

In an eighth aspect of the invention, the sugar structure for theα-selective glycosylation according to any one of the first to seventhaspects of the invention has a substituent at position 2, thesubstituent interfering with the α-selective glycosylation throughneighboring group participation.

One particular advantage of the actions and advantages of the firstaspect of the invention is to secure highly selective α-glycosylationeven for such sugar structure with a substituent at position 2, thesubstituent highly interfering with the α-selective glycosylationthrough the neighboring group participation during general glycosylationreactions.

In a ninth aspect of the invention, the substituent at position 2according to the α-selective glycosylation in the eighth aspect is anamino group bound to Troc group or acetyl group.

In case that the substituent at position 2 in the sugar structure is anamino group bound to Troc group or acetyl group (including amino groupsmodified with Troc group or acetyl group according to the sixth aspector the seventh aspect), generally, stronger neighboring groupparticipation occurs. As described above, additionally, the neighboringgroup participation has been a serious disadvantage for the chemicalsynthesis of glycoproteins of O linkage type. In such case, therefore,the α-selective glycosylation process according to the first aspect isvery advantageous.

In a tenth aspect of the invention, use is made of amino acids withalcoholic hydroxyl group or thiol group, and peptide chains,monosaccharides or disaccharides to oligosaccharides or sugar chainscontaining any one of such amino acids as constituent residues, as theacceptor compounds for the α-selective glycosylation according to anyone of the first to ninth aspects of the invention.

Any acceptor compound with alcoholic hydroxyl group or thiol group issatisfactory as the acceptor compound for use in the α-selectiveglycosylation process, with no specific limitation. Any of the compoundsdefined in the tenth aspect is preferably listed.

The above and other advantages of the invention will become moreapparent in the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of an α-selective glycosylation process accordingto a previous technique.

FIG. 2 is a flow chart of an α-selective glycosylation process accordingto a previous technique.

FIG. 3 is a chart depicting the α-selective glycosylation processaccording to an example of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Modes for carrying out the invention are now described below, includingbest embodiments of the invention. The term “present invention” simplyreferred to hereinbelow means the individual inventions in thisapplication.

[α-Selective Glycosylation Process]

The α-selective glycosylation process of the invention is done by aprocess of glycosylation between a sugar structure (sugar donor) and acompound with alcoholic hydroxyl group or thiol group (sugar acceptor).The characteristic feature thereof includes the ring-shaped formation ofa protective group in a silyl acetal structure over hydroxyl groups atpositions 4 and 6 in a sugar structure and the subsequent glycosylationbetween the sugar structure and an acceptor compound. Consequently, sohighly α-selective glycosylation process can be progressed that theresulting sugar structure glycoside contains α-glycoside at a ratio of80% or more in the ratio of α- /β-glycosides.

For forming the protective group in the silyl acetal structure,preferably, given reactive functional groups except the hydroxyl groupsat positions 4 and 6 in the sugar structure are preliminarily treatedwith protective group modification because of the various reasonsdescribed in the section of advantages and actions of the eighth aspectof the invention. The types of the reactive functional groups to bepreliminarily treated with protective group modification and thepositions thereof in the sugar structure are not limited but areappropriately treated with protective group modification on a neededbasis. Typically, the amino group or hydroxyl group at position 2 in thesugar structure and the hydroxyl group at position 3 therein are treatedwith protective group modification.

The protective group for the amino group at position 2 includes forexample general acyl-series protective groups such as acetyl group,trihaloacetyl group, levulinoyl group, phthaloyl group and Troc group.The protective group for the hydroxyl group at position 2 includes forexample general acyl-series protective groups such as acetyl group,monohaloacetyl group, dihaloacetyl group, levulinoyl group, benzoylgroup, and pivaloyl group. The protective group for the hydroxyl groupat position 3 includes for example etheric protective groups such asbenzyl group, p-methoxybenzyl group and allyl group in addition toacyl-series protective groups such as acetyl group, benzoyl group andpivaloyl group. Among the individual protective groups, many of theprotective groups for the amino group or hydroxyl group at position 2exert strong neighboring group participation in general glycosylationreactions and adversely work for α-selective glycosylation. In theα-selective glycosylation process in accordance with the invention asdescribed above, however, such serious disadvantage never occurs.

[Reaction Conditions and the Like for α-Selective Glycosylation Process]

For the α-selective glycosylation process in accordance with theinvention, for example, the reaction conditions, the concentrations ofthe donor and the acceptor in the reaction system and the use ofreaction catalysts are not specifically limited but are appropriatelydesigned if necessary.

Herein, the reaction conditions are preferably as follows. Using anon-polar solvent such as methylene chloride, the glycosylation is doneat a reaction temperature within a range of −30° to 0° C. Theconcentrations of the donor and the acceptor in the reaction system arepreferably about 0.1 M. The concentration ratio of the donor and theacceptor in the reaction system is essentially determined in astoichiometric manner. Preferably, the donor at about 1.5 equivalentmoles of the acceptor is used.

[Sugar Structure]

The sugar structure for use in accordance with the invention is a sugarstructure of hexose or an aldose having a chain with seven or morecarbon atoms in the molecule, the sugar structure containing hydroxylgroups at least at positions 4 and 6 and satisfying the constitutionalconditions such that the hydroxyl group at position 4 is in the axialbond and a group at position 5 is in the equatorial bond. The sugarstructure may be used as a monosaccharide or as a reducing end of adisaccharide to an oligosaccharide or a sugar chain. As long as thesugar structure satisfies the conditions described above, the typethereof is not specifically limited. However, the sugar structure typetypically includes any one of those described below as (a) to (d). Anyone of them is described on a concept including derivatives thereof withappropriate substituents introduced at any position, for examplederivatives with substituents, such as D/L-galactose with a substituent,for example N-acetylgalactosamine.

-   (a) D-Galactose or L-galactose-   (b) D-Gulose or L-gulose-   (c) 2-Deoxy-D-galactose or 2-deoxy-L-galactose-   (d) Heptose with an essential structure of any one of (a) through    (c).

Based on the reasons described in the section of advantages and actionsof the third aspect of the invention, these sugar structures when theyare in the D form preferably take a C1 steric conformation of asix-membered ring (⁴C₁ pyranoside structure) or these sugar structureswhen they are in the L form preferably take a 1C steric conformation ofa six-membered ring (¹C₄ pyranoside structure). It cannot be denied thatsugar structures never falling under the conditions may possibly beused.

[Formation of Protective Group in Silyl Acetal Structure]

Any protective group in the silyl acetal structure is satisfactory asthe ring-shaped protective group formed over the hydroxyl groups atpositions 4 and 6 in the sugar structure, with no specific limitation.Dialkylsilylene group is particularly preferably listed. Specifically,di-(t-butyl)-silylene group (DTBS group) is listed preferably.Additionally, for example, di-isopropyl-silylene group,di-isobutyl-silylene group, di-n-butyl-silylene group anddi-n-propyl-silylene group are preferably listed.

[Acceptor Compound]

Any organic compound with alcoholic hydroxyl group or thiol group isessentially satisfactory as the acceptor compound for use in accordancewith the invention. Preferably, the acceptor compound is an amino acidwith alcoholic hydroxyl group or thiol group, for example serine,threonine and cysteine. Because the invention relates to one of organicsynthetic processes, it is needless to say that both L-amino acid andD-amino acid can be used.

Further, peptide chains (oligopeptide or polypeptide) containing any oneof the amino acids as the constitutional residues are preferably listedas the acceptor compound. Monosaccharides, or disaccharides tooligosaccharides or sugar chains are also preferably listed.

Still further, general organic alcohol compounds or thiol compoundsincluding for example methyl alcohol, ethyl alcohol, and ethyl mercaptanother than those described above, may also be used as the acceptorcompounds.

Embodiments

Examples of the invention are described below. These Examples neverlimit the technical scope of the invention.

EXAMPLE 1 Synthesis of Acceptor Compound

First, the carboxyl group in a sialic acid dimer of the followingchemical formula 1 as obtained from colominic acid was prepared intomethyl ester, to obtain a sialic acid dimer represented by the followingchemical formula 2. In that case, the carboxyl group at its non-reducingend was allowed to form lactone together with the hydroxyl group atposition 8 at the reducing end. Further, the acetyl group at theanomeric position in the sialic acid dimer represented by the chemicalformula 2 was converted to phenylthio group (SPh group), to obtaindisialyl galactose represented by the following chemical formula 3. Inthe chemical formulas 1 through 3, herein, “Ac” means acetyl group and“Sph” means phenylthio group.

Then, galactose modified with a protective group as shown in thefollowing chemical formula 4 was separately prepared. In the chemicalformula 4, “Bn” means benzyl group and “SE” means2-(trimethylsilyl)ethyl group.

Subsequently, the disialyl galactose represented by the chemical formula3 was condensed with the galactose represented by the chemical formula4, under given reaction conditions considered suitable on the basis ofthe examination of the reaction conditions. The α-isomer represented bythe chemical formula 5 below was separated from a mixture of the α- andβ-steric isomers thus generated, by silica gel chromatography using agiven composition of an eluent. The compound represented by the chemicalformula 5 was used as the acceptor compound for use in the α-selectiveglycosylation process in accordance with the invention.

The α-isomer represented by the chemical formula 5 is2-(trimethylsilyl)ethyl[methyl5-acetamide-8-O-(5-acetamide-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosilono-1′,9-lactone)-4,7-di-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosilonate]-(2→3)-2,6-di-O-benzyl-β-D-galactopyranoside.

EXAMPLE 2 Synthesis of Sugar Structure

First, a galactosamine triol derivative represented by the followingchemical formula 6 was prepared by a predetermined synthetic process,where the hydroxyl group at position 1 was protected with Sph group andthe amino group at position 2 was protected with Troc group. Thegalactosamine triol derivative has the “⁴C₁” pyranoside structure.

Using DTBS (OTf)₂ with trifluoromethanesulfonic acid as an eliminationgroup attached to di-t-butylsilane, then, DTBS was introduced into thepositions 4 and 6 in the compound represented by the chemical formula 6under predetermined reaction conditions, to obtain a compound of thefollowing chemical formula 7, having the protective group in the silylacetal structure at the positions 4 and 6.

Further, TrocC1 reacted with the compound represented by the chemicalformula 7 in a pyridine solvent, to obtain a compound represented by thefollowing chemical formula 8, where Troc group was introduced at theposition 3. The compound of the chemical formula 8 was used as a sugarstructure (galactosamine donor) for use in the α-selective glycosylationprocess in accordance with the invention.

The compound represented by the chemical formula 8 is phenyl2-deoxy-4,6-O-di-tert-butylsilylene-1-thio-3-O-(2,2,2-trichloroethoxycarbonyl)-2-(2,2,2-trichloroethoxycarbonylamino)-β-D-galactopyranoside.

EXAMPLE 3 Glycosylation

As shown in FIG. 3, glycoside represented by the following chemicalformula 9 was obtained from the sugar structure of the chemical formula8 and the acceptor compound of the chemical formula 5, by the processdescribed below.

The glycoside of the chemical formula 9 is2-(trimethylsilyl)ethyl[methyl5-acetamide-8-O-(5-acetamide-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galadto-2-nonulopyranosilono-1′,9-lactone)-4,7-di-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosilonate-(2→3)]-[2-deoxy-4,6-O-di-tert-butylsilylene-3-O-(2,2,2-trichloroethoxycarbonyl)-2-(2,2,2-trichloroethoxycarbonylamino)-α-D-galactopyranosyl]-2,6-di-O-benzyl-β-D-galactopyranoside.

Specifically, the sugar structure of the chemical formula 8 (118 mg,0.155 mmol) and the acceptor compound of the chemical formula 5 (100 mg,77.4 μmol) were dissolved in 5.0 ml of dichloromethane, to which MS4A°(200 mg) was added, for agitation at ambient temperature for one hour.Subsequently, the resulting mixture was cooled to 0° C., to whichN-iodosuccinimide (NIS) of 70 mg, i.e. 0.310 mmol andtrifluoromethanesulfonic acid (TfOH) of 2.7 μl, i.e. 31.0 μmol wereadded for agitation.

Under observations of the progress of the reaction by thin-layerchromatography (TLC), the sugar structure of the chemical formula 8 (118mg), NIS (70 mg) and TfOH (2.7 μl) were again individually added once.In total, the agitation was done for 32 hours.

The termination of the reaction was confirmed by TLC (AcOEt/MeOH= 15/1).The generated solids were filtered off through Celite and washed withchloroform. The filtrate and the washing solution were combined togetherand diluted with chloroform. The organic layer was rinsed sequentiallywith sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried and concentrated overNa₂SO₄. The resulting syrup was subjected to column chromatography.Glycoside of the chemical formula 9 (113 mg, 75%) was obtained from theresulting elution solvent.

[Discussions About Examples 1 Through 3]

The Examples 1 through 3 were parts of experiments intended for thepurpose of synthetically preparing disialylgalactose unit. The inventorsspeculated that because the amino group at position 2 in the sugarstructure of the chemical formula 8 was Troc group with possibleneighboring group participation, β-glycoside would be obtained from thesugar structure of the chemical formula 8 and the acceptor compound ofthe chemical formula 5.

However, the resulting glycoside of the chemical formula 9 wasunexpectedly α-glycoside according to the analysis by ¹H-NMR. Not anypossible β-glycoside product was confirmed. As shown below in Table 1,additionally, synthetic experiments with the same contents as in Example3 except for slight modifications of the reaction temperature, theconcentrations of the donor and the acceptor and the reaction time werecarried out (Example 3 described above corresponds to Entry No. 1 inTable 1). In any of the Examples of such synthetic experiments, onlyα-glycoside was obtained at yields shown in Table 1, with noconfirmation of any product considered as β-glycoside.

TABLE 1 Entry Temp. Conc. Time Yield 1 0° C.  46 mM 32 h (75%) 2 0° C.300 mM 32 h (68%) 3 −30° C.→0° C. 300 mM 117 h  (70%)

In the column of yield in Table 1 (the column “Yield”), the numericalfigures representing percentage ratios are expressed in parenthesis,because impure signals of possible rotamers are contaminated as observedby ¹H-NMR. The cause of such phenomenon is not discussed in detail.However, it was suggested that the impure signals emerged due to theinfluence of the DTBS group.

A novel synthetic approach very simple and advantageous for example forchemical synthesis of sugar chains of O linkage type and the like can beprovided, owing to the achievement of the highly selectiveα-glycosylation process in the synthetic systems as in Examples 1through 3. The development of an improved potential synthetic processfor the chemical synthesis thereof was desired in the past. So as toverify which element enabled the α-selective glycosylation in Examples 1through 3, the following Examples 4 through 6 and Comparative Example 1were continuously carried out.

EXAMPLE 4 Change of Acceptor Compound (1)

Using 2-adamantanl (represented by the following chemical formula 10)with less steric hindrance against glycosylation as an acceptorcompound, an attempt was made to introduce a sugar structure donor intothe hydroxyl group thereof in the following manner.

Specifically, the sugar structure of the chemical formula 8 (50 mg, 65.6μmol) and 2-adamantanol of the chemical formula 10 (30 mg, 0.197 mmol)as an acceptor compound were dissolved in 2.6 ml of dichloromethane, towhich MS4A° (80 mg) was added, for agitation at ambient temperature forone hour. Subsequently, the resulting mixture was cooled to 0° C., towhich NIS (30 mg, 0.131 mmol) and TfOH (1.2 μl, 13.1 μmol) were addedfor agitation for one hour.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=⅓).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography.

Then, glycoside from the condensation was obtained from the resultingelution solvent (AcOEt/hexane= 1/20) of the column chromatography. Theglycoside was structurally analyzed (by ¹H-NMR; the same is truehereinbelow). Although β-glycoside was observed at about 8%, α-glycosidewas obtained at a yield of 85%.

EXAMPLE 5 Change of Acceptor Compound (2)

For the application of the invention to sugar, an attempt was made tointroduce a sugar structure donor into the hydroxyl group at position 6in a primary alcohol glucose (represented by the chemical formula 11)used as an acceptor compound in the following manner.

Specifically, the sugar structure of the chemical formula 8 (50 mg, 65.6μmol) and the compound of the chemical formula 11(n-hexyl-2,3,4-tri-O-acetyl-β-D-glucopyranoside; 38 mg, 98.4 μmol) as anacceptor compound were dissolved in 2 ml of dichloromethane, to whichMS4A° (100 mg) was added, for agitation at ambient temperature for onehour. Subsequently, the resulting mixture was cooled to 0° C., to whichNIS (30 mg, 0.131 mmol) and TfOH (1.2 μl, 13.1 μmol) were added foragitation for 5 hours.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=½).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography.

Then, glycoside from the condensation was obtained from the resultingelution solvent (AcOEt/hexane=¼) of the column chromatography. Theglycoside was analyzed structurally. Surprisingly, α-glycoside wasobtained at a yield as high as 90%. Some spot of possible β-glycosidewas observed on TLC. However, the spot could not be isolated oridentified.

EXAMPLE 6 Change of Protective Group at Position 3 in Sugar Structure

So as to demonstrate the influence of a protective group at position 3in a sugar structure, the compound represented by the chemical formula12 was used as a sugar structure donor, where Troc group as theprotective group at position 3 in the sugar structure of the chemicalformula 8 was replaced with acetyl group of the same acyl series. Anattempt was made to introduce the sugar structure donor into thehydroxyl group at position 6 in the glucose acceptor of the chemicalformula 11 as in Example 5, in the following manner.

Specifically, the sugar structure of the chemical formula 12 (50 mg,79.5 μmol) and the compound of the chemical formula 11 (47 mg, 0.119mmol) as an acceptor compound were dissolved in 2 ml of dichloromethane,to which MS4A° (100 mg) was added, for agitation at ambient temperaturefor one hour. Subsequently, the resulting mixture was cooled to 0° C.,to which NIS (36 mg, 0.159 mmol) and TfOH (1.4 μl, 15.9 μmol) were addedfor agitation for 30 minutes.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=½).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography.

Then, the compound represented by the chemical formula 13 was obtainedfrom the resulting elution solvent (AcOEt/hexane=¼) of the columnchromatography. The yield was 69 mg, which was almost quantitative at ayield as high as 96%. The result is surprising.

COMPARATIVE EXAMPLE 1 Use of Sugar Structure with No Protection withDTBS Group

As a sugar structure donor with no protective group in the silyl acetalstructure over the hydroxyl groups at positions 4 and 6 in the sugarstructure, the compound represented by the following chemical formula 14[3,4,6-tri-O-acetyl-2-deoxy-1-thio-2-(2,2,2-trichloroethoxycarbonylamino)-β-D-galactopyranoside]was used. In the following manner, an attempt was made to progress theglycosylation of the sugar structure with an acceptor compoundrepresented by the chemical formula 5.

Specifically, the sugar structure of the chemical formula 14 (1.10 g,1.93 mmol) and the compound of the chemical formula 5 (1.00 g, 0.774mmol) as an acceptor compound were dissolved in 77 ml ofdichloromethane, to which MS4A° (2 g) was added, for agitation atambient temperature for one hour. Subsequently, the resulting mixturewas cooled to 0° C., to which NIS (868 mg, 3.86 mmol) and TfOH (34 μl,0.386 mmol) were added for agitation for one hour.

The termination of the reaction was confirmed by TLC (AcOEt/MeOH= 15/1).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography.

Then, the glycoside represented by the chemical formula 15 was obtainedat a yield of 994 mg and 73% from the resulting elution solvent (AcOEt)of the column chromatography. The glycoside was structurally analyzed.It was found that the glycoside was β-glycoside.

[Discussion About Examples 4 Through 6 And Comparative Example 1]

The results of Examples 4 and 5 were discussed together with the resultsof Example 3. It is determined that the type or chemical structure ofthe acceptor compound is not an element defining the possibility ofα-selective glycosylation. Thus, satisfactorily, the acceptor compoundapplicable for the α-selective glycosylation in accordance with theinvention has an alcoholic hydroxyl group or thiol group as thecondition as the acceptor compound for general glycosylation reactions.

The results of Example 6 then indicate that the type of the protectivegroup at position 3 in the sugar structure is not an element definingthe possibility of the α-selective glycosylation.

While the total or almost the total amount of the glycosides generatedin the individual Examples were α-glycosides, the whole amount of thegenerated glycosides was β-glycoside, only when a sugar structure donorwith no protective group in the silyl acetal structure over the hydroxylgroups at positions 4 and 6 was used as in Comparative Example 1.Therefore, the element defining the possible occurrence of theα-selective glycosylation in accordance with the invention is “thering-shaped formation of a protective group in a silyl acetal structureover the hydroxyl groups at positions 4 and 6 in a sugar structuredonor”.

EXAMPLE 7 Neighboring Group Participation of Protective Group atPosition 2 in Aminosugar Donor (1)

As described above concerning the related art, the neighboring groupparticipation of the protective group of amino group at position 2 was aserious drawback against the intended α-selective introduction ofgalactosamine and glucosamine with amino group at position 2 intoacceptor compounds. So as to examine whether or not α-selectiveglycosylation could be progressed even when the Troc group as aprotective group of amino group at position 2 in the sugar structurerepresented by the chemical formula 8 was replaced with a protectivegroup with approved stronger neighboring group participation than theTroc group, therefore, Example 7 was done below.

Using a compound of the following chemical formula 16 as prepared byreplacing the Troc group at position 2 in the compound of the chemicalformula 8 with Bz group (practically, the Troc group at position 3 wassimilarly replaced in the same manner) as a sugar structure donor, anattempt was made to introduce the sugar structure donor into thehydroxyl group at position 6 in the glucose acceptor of the chemicalformula 11 as in Example 5, in the following manner.

Specifically, the sugar structure of the chemical formula 16 (50 mg,80.5 μmol) and the compound of the chemical formula 11 (47 mg, 0.121mmol) as an acceptor compound were dissolved in 2 ml of dichloromethane,to which MS4A° (100 mg) was added, for agitation at ambient temperaturefor one hour. Subsequently, the resulting mixture was cooled to 0° C.,to which NIS (36 mg, 0.161 mmol) and TfOH (1.4 μl, 16.1 μmol) were addedfor agitation for 20 hours.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=½).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography.

Then, the α-glycoside compound represented by the following chemicalformula 17 (verified by structural analysis) was obtained from theresulting elution solvent (AcOEt/hexane=⅕) of the column chromatography.The yield was 51 mg at 71%. β-Glycoside was never isolated. Slightamounts of some byproducts were generated.

EXAMPLE 8 Neighboring Group Participation of Protective Group atPosition 2 in Aminosugar Donor (2)

Due to the same reason as in Example 7, the Troc group as a protectivegroup of the amino group at position 2 in the sugar structurerepresented by the chemical formula 8 was replaced with Phth group withapparently approved stronger neighboring group participation than theTroc group (Troc group at position 3 was also replaced with acetylgroup, actually), to prepare a compound of the following chemicalformula 18, which was used as a sugar structure donor for an attempt tointroduce the resulting sugar structure donor into the hydroxyl group atposition 6 in the glucose acceptor of the chemical formula 11 as inExample 5.

The sugar structure of the chemical formula 18 (100 mg, 0.171 mmol) andthe compound of the chemical formula 11 (100 mg, 0.256 mmol) as anacceptor compound were dissolved in 4.3 ml of dichloromethane, to whichMS4A° (200 mg) was added, for agitation at ambient temperature for onehour. Subsequently, the resulting mixture was cooled to 0° C., to whichNIS (77 mg, 0.342 mmol) and TfOH (3 μl, 34.2 μmol) were added foragitation for 30 minutes.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=½).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography.

Then, the α-glycoside compound represented by the chemical formula 19(confirmed by structural analysis) was obtained from the resultingelution solvent (AcOEt/hexane=⅖) of the column chromatography. The yieldwas 141 mg at 95%.

[Discussion About Examples 7 and 8]

Based on the results of Examples 7 and 8, it was confirmed that theα-selective glycosylation process in accordance with the invention wasestablished with no influence of the intensity of neighboring groupparticipation, which has been a problem in the related art. Thus, it wasconfirmed that the process was a highly applicable process.

EXAMPLE 9 Synthesis of α-galactosamine-serine

As described above, the highly applicable α-selective glycosylation ofthe sugar structure donor of galactose type is the chemical synthesis ofa sugar chain of O linkage type. In α-galactosamine-L-serine andα-galactosamine-L-threonine composing the peptide linkage site between asugar chain of O linkage type and a peptide, the latter was selected foran attempt of the α-selective glycosylation process, as described below.

First, a sugar structure of the chemical formula 8 and with introducedTroc group at position 3 was used, taking account of subsequentextension of the sugar chain. Concerning the serine side, two types ofprotective groups introduced therein as represented by the chemicalformulas 20 and 21 were prepared, taking account of subsequent extensionof the peptide chain. As described below in Examples 9-1 and 9-2, somedifference in yield was observed, depending on the difference in theprotective groups of the amino acid. In any of the cases, highα-selectivity was expressed as expected.

EXAMPLE 9-1

The sugar structure of the chemical formula 8 (122 mg, 0.160 mmol) andthe compound of the chemical formula 20(N-benzyloxycarbonyl-L-serine-pentafluorophenyl ester; 50 mg, 0.123mmol) as an acceptor compound were dissolved in 2.8 ml ofdichloromethane, to which MS4A° (170 mg) was added, for agitation atambient temperature for one hour. Subsequently, the resulting mixturewas cooled to 0° C., to which NIS (72 mg, 0.320 mmol) and TfOH (2.8 μl,32.0 μmol) were added for agitation for 30 minutes.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=½).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat: Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography.

Then, the expected α-glycoside, i.e. α-galactosamine-serine (confirmedby structural analysis) was obtained from the resulting elution solvent(AcOEt/hexane=⅓) of the column chromatography. The yield was 117 mg at90%.

EXAMPLE 9-2

The sugar structure of the chemical formula 8 (100 mg, 0.131 mmol) andthe compound of the chemical formula 21(N-9-fluorenylmethoxycarbonyl-L-serine-pentafluorophenyl ester; 50 mg,0.101 mmol) as an acceptor compound were dissolved in 2.3 ml ofdichloromethane, to which MS4A° (150 mg) was added, for agitation atambient temperature for one hour. Subsequently, the resulting mixturewas cooled to 0° C., to which NIS (59 mg, 0.262 mmol) and TfOH (2.3 μl,26.2 μmol) were added for agitation for 30 minutes.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=½).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography.

Then, the expected α-glycoside, i.e. α-galactosamine-serine (confirmedby structural analysis) was obtained from the resulting elution solvent(AcOEt/hexane=⅓) of the column chromatography. The yield was 91 mg at78%.

EXAMPLE 10 Change of Protective Group at Position 1 in Sugar Structure

Using sugar structures prepared by individually replacing the protectivegroup (Sph group) of the hydroxyl group at position 1 in the sugarstructure of the chemical formula 8 with SCH₃ group (I), F group (Ro)and OC(NH)CCl₃ group (Ha), an α-selective glycosylation process betweenone of the resulting sugar structures and 2-adamantanol was progressed.

EXAMPLE 10-1

The sugar structure (I) (150 mg, 0.214 mmol) and 2-adamantanol (21.7 mg,0.143 mmol) were dissolved in 3.5 ml of dichloromethane under argonpurging, to which MS4A° (170 mg) was added, for agitation at ambienttemperature for one hour. Subsequently, the resulting mixture was cooledto 0° C., to which NIS (96.4 mg, 0.428 mmol) and TfOH (3.8 μl, 42.8μmol) were added for agitation for 30 minutes.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=⅓).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. Na₂CO₃, sat. Na₂S₂O₃, and brine, dried andconcentrated over Na₂SO₄. The resulting syrup was subjected to columnchromatography. Then, the glycoside obtained from the resulting elutionsolvent (AcOEt/hexane= 1/30) was analyzed structurally. Althoughβ-glycoside was observed at about 11% (13 mg), α-glycoside was obtainedat a yield of 85% (106 mg).

EXAMPLE 10-2

The sugar structure (Ro) (150 mg, 0.223 mmol) and 2-adamantanol (22.6mg, 0.148 mmol) were dissolved in 3.7 ml of dichloromethane under argonpurging, to which MS4A° (170 mg) was added, for agitation at ambienttemperature for one hour. Subsequently, the resulting mixture was cooledto 0° C., to which SnCl₂ (42.3 mg, 0.223 mmol) and AgClO₄ (55.5 mg,0.267 mmol) were added in darkness for agitation for 16 hours.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=¼).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. NaHCO₃, and brine, dried and concentrated overNa₂SO₄. The resulting syrup was subjected to silica gel columnchromatography. Then, the glycoside obtained from the resulting elutionsolvent (AcOEt/hexane= 1/30) was analyzed structurally. Althoughβ-glycoside was observed at about 10% (12 mg), α-glycoside was obtainedat a yield of 78% (93 mg).

EXAMPLE 10-3

The sugar structure (Ha) (150 mg, 0.184 mmol) and 2-adamantanol (18.7mg, 0.123 mmol) were dissolved in 3.1 ml of dichloromethane in argonpurging, to which AW-300 (170 mg) was added, for agitation at ambienttemperature for one hour. Subsequently, the resulting mixture was cooledto 0° C., to which TMSOf (0.670 μl, 3.68 μmol) was added for agitationfor 30 minutes.

The termination of the reaction was confirmed by TLC (AcOEt/hexane=⅓).The generated solids were filtered off through Celite and washed withchloroform. Further, the filtrate and the washing solution were combinedtogether and diluted with chloroform. The organic layer was rinsedsequentially with sat. NaHCO₃, and brine, dried and concentrated overNa₂SO₄. The resulting syrup was subjected to silica gel columnchromatography. Then, the glycoside obtained from the resulting elutionsolvent (AcOEt/hexane= 1/30) was analyzed structurally. Althoughβ-glycoside was observed at about 9% (9 mg), α-glycoside was obtained ata yield of 87% (86 mg).

While the preferred embodiments have been described, variations theretowill occur to those skilled in the art within the scope of the presentinventive concepts, which are delineated by the following claims.

The invention claimed is:
 1. An α-selective glycosylation processbetween a donor compound having a sugar structure and an acceptorcompound having an alcoholic hydroxyl group or thiol group comprising,(1) the step of providing a sugar structure of hexose or an aldosehaving a chain with six carbon atoms in the molecule which is amonosaccharide or a reducing end of an oligosaccharide having two ormore monosaccharide residues or a sugar chain, which sugar structuresatisfies the constitutional conditions such that the sugar structurehas hydroxyl groups at positions 4 and 6 and that the hydroxyl group atposition 4 is in an axial bond and a group at position 5 is inequatorial bond, wherein the sugar structure is substituted with aminoat position 2, the amino being bound to a 2,2,2-trichloroethoxycarbonylgroup, the sugar structure having a hydroxyl group at the 3-positionthat is protected with a group selected from among an acetyl group, abenzoyl group, a pivaloyl group, a benzyl group, a p-methoxybenzyl groupand an allyl group, (2) a step of forming a protective group in a silylacetal structure in a ring shape over the hydroxyl groups at positions 4and 6 in the sugar structure, and (3) a step of promoting theglycosylation between the sugar structure and the alcoholic hydroxylgroups or thiol group of the acceptor compound, and (4) a step ofpreparing a sugar structure glycoside containing α-glycoside at a ratioof 80% or more in the ratio of α-/β-glycosides, wherein the acceptorcompound is selected from the group consisting of serine, threonine,cystine, peptides, mono or oligogalactopyranosides, and mono oroligoglucopyranosides.
 2. An α-selective glycosylation process accordingto claim 1, where the protective group in the silyl acetal structure isa dialkylsilylene group.
 3. An α-selective glycosylation processaccording to claim 2, where the dialkylsilylene group isdi-(t-butyl)-silylene group (DTBS group).
 4. An α-selectiveglycosylation process according to claim 2, where the dialkylsilylenegroup is di-isopropyl-silylene group, di-isobutyl-silylene group,di-n-butyl-silylene group or di-n-propyl-silylene group.
 5. Anα-selective glycosylation process according to claim 1, where reactivefunctional groups except the hydroxyl group at positions 4 and 6 in thesugar structure are preliminarily treated with protective groupmodification before the formation of the protective group silylacetalstructure.
 6. A process for glycosylation of a glycosylation acceptorhaving an alcoholic hydroxyl group or a thiol group with a glycosylationdonor, wherein the glycosylation donor comprises a pyranoside structure,derivable from an aldose having six carbon atoms, having anequatorially-positionable hydroxyl group at the 4-position of thepyranoside structure, an axially-positionable hydroxymethyl orhydroxymethylene group at the 5-position of the pyranoside structure,and amino at the 2-position of the pyranoside structure, the amino beingbound to a 2,2,2-trichloroethoxycarbonyl group, the pyranoside structurehaving a hydroxyl group at the 3-position that is protected with a groupselected from among an acetyl group, a benzoyl group, a pivaloyl group,a benzyl group, a p-methoxybenzyl group and an allyl group, and furtherwherein the glycosylation donor is a monosaccharide, a disaccharide, oran oligosaccharide, the α-selective glycosylation process comprising thesteps of a) forming a cyclic silyl acetal group bridging theequatorially-positionable hydroxy group at the 4-position of thepyranoside structure and the hydroxyl group of the axially-positionablehydroxymethyl or hydroxymethylene group at the 5-position of thepyranoside structure so as to form a bicyclo [6.6.0.] structure, and b)glycosylating the alcoholic hydroxyl group or thiol group of theglycosylation acceptor to form glycosylated product, whereby the ratioof α-glycosylated product to β-glycosylated product is at 4:1.
 7. Theprocess of claim 6 wherein the pyranoside structure is selected from thegroup consisting of glucopyranoside, galactopyranoside,2-amino-2-deoxyglucopyranoside, and 2-amino-2-deoxygalactopyranoside. 8.The process of claim 6 wherein the glycosylation acceptor comprises aglycoside moiety having an alcoholic hydroxyl group at its 6-position.9. The process of claim 6 wherein the glycosylation acceptor is selectedfrom the group consisting of: galactopyranosides having a hydroxyl groupat the 4-position, glucopyranosides having a hydroxyl group at the 6-position, serine, threonine, and cysteine.
 10. The process of claim 9wherein the pyranoside structure is selected from the group consistingof glucopyranoside, galactopyranoside, 2-amino-2-deoxyglucopyranoside,and 2-amino-2-deoxygalactopyranoside.
 11. An α-selective glycosylationprocess comprising promoting glycosylation between a sugar structure andan acceptor compound, wherein the sugar structure is substituted withamino at position 2, the amino being bound to a2,2,2-trichloroethoxycarbonyl group, the sugar structure having hydroxylgroups at positions 4 and 6, and having a protective group of a silylacetal structure in a ring shape over the hydroxyl groups at positions 4and
 6. 12. The α-selective glycosylation process of claim 11 wherein thesugar structure is hexose or an aldose having a chain with six carbonatoms and the acceptor compound has an alcoholic hydroxyl group or thiolgroup, the sugar structure being a monosaccharide or a reducing end ofan oligosaccharide having two or more monosaccharide residues or a sugarchain, the hydroxyl group at position 4 being in an axial bond and agroup at positon 5 being in an equatorial bond, the sugar structurehaving a hydroxyl group at the 3-position that is protected with a groupselected from among an acteyl group, a benzoyl group, a pivaloyl group,a benzyl group, a p-methoxybenzyl group and an allyl group.
 13. Theα-selective glycosylation process of claim 11 wherein the acceptorcompound is selected from the group consisting of serine, threonine,cystine, peptides, mono- or oligogalactopyranosides, and mono oroligoglucopyranosides.
 14. The α-selective glycosylation process ofclaim 12 wherein the acceptor compound is selected from the groupconsisting of serine, threonine, cystine, peptides, mono- oroligogalactopyranosides, and mono or oligoglucopyranosides.
 15. Theα-selective glycosylation process according to claim 11, where theprotective group of the silyl acetal structure is a dialkylsilylenegroup.
 16. The α-selective glycosylation process according to claim 15,where the dialkylsilylene group is di-(t-butyl)-silylene group (DTBSgroup).
 17. The α-selective glycosylation process according to claim 15,where the dialkylsilylene group is di-isopropyl-silylene group,di-isobutyl-silylene group, di-n-butyl-silylene group ordi-n-propyl-silylene group.
 18. The α-selective glycosylation processaccording to claim 11, where reactive functional groups except thehydroxyl groups at positions 4 and 6 in the sugar structure arepreliminarily treated with protective group modification before theformation of the protective group in the silyl acetal structure.
 19. Aprocess for the glycosylation of a glycosylation acceptor comprisingpromoting the glycosylation between a glycosylation donor comprising apyranoside structure and a glycosylation acceptor, wherein thepyranoside structure is substituted with amino at the 2-position that isbound to a 2,2,2-trichloroethoxycarhonyl group, and having a cyclicsilyl acetal group bridging an equatorially-positionable hydroxy groupat 4-position of the pyranoside structure and a hydroxyl group of theaxially-positionable hydroxymethyl or hydroxymethylene group at the5-position of the pyranoside structure so as to form a bicyclo [6.6.0.]structure.
 20. The process for the glycosylation of a glycosylationacceptor of claim 19 wherein the pyranoside structure is derivable froman aldose having six carbon atoms, the pyranoside structure having anequatorially-positionable hydroxyl group at the 4-position, anaxially-positionable hydroxymethyl or hydroxymethylene group at the5-position, a hydroxyl group at the 3-position protected with a groupselected from among an acetyl group, a benzoyl group, a pivaloyl group,a benzyl group, a p-methoxybenzyl group and an allyl group, and furtherwherein the glycosylation donor is a monosaccharide, a disaccharide, oran oligosaccharide.
 21. The process for the glycosylation of aglycosylation acceptor of claim 20 further comprising glycosylating thealcoholic hydroxyl group or thiol group of the glycosylation acceptor toform glycosylated product.
 22. The process of claim 19 wherein thepyranoside structure is selected from the group consisting ofglucopyranoside, galactopyranoside, 2-amino-2-deoxyglucopyranoside, and2-amino-2-deoxygalactopyranoside.
 23. The process of claim 19 whereinthe glycosylation acceptor comprises a glycoside moiety having analcoholic hydroxyl group at its 6-position.
 24. The process of claim 19wherein the glycosylation acceptor is selected from the group consistingof galactopyranosides having a hydroxyl group at the 4-position,glucopyranosides having a hydroxyl group at the 6-position, serine,threonine, and cysteine.
 25. The process of claim 19 wherein thepyranoside structure is selected from the group consistingglucopyranoside, galactopyranoside, 2 amino-2 -deoxyglucopyranoside, and2-amino-2-deoxygalactopyranoside.